Pilot light apparatus

ABSTRACT

A system for providing a pilot light to the upper burner of a two burner oven including an air entrainment chamber supplied with fresh air by a vertical tube open at its lower end. Outstandingly high air-to-gas ratios are achieved by selfproducing noise to disturb a jet stream of natural gas emanating from a nozzle. One important construction is the use of an approximately rectangular electric discharge machined nozzle orifice having a length-to-width ratio greater than about 3:1.

United States Patent 91 Grayson et al. Nov. 6, 1973 PILOT LIGHT APPARATUS 3,376,862 4/1968 Riehl 126/39 E [75] Inventors: Richard D. Grayson, Arcadia; John W. Dobson, Burbank; Happy H. Primary ExaminerCarroll B. Dorit Jr.

. y Unfried, Northridge, all of Calif. Attorney-C. Cornell Remsen, Jr., Walter J. Baum, [73] Assignee: international Telephone and agi g:' iggsg gigg Johnson and Telegraph Corporation, New York, N.Y.

[22] Filed: Feb. 18, 1970 [57] ABSTRACT [21] Appl. No.: 12,402 A system for providing a pilot light to the upper burner of a two burner oven including an air entrainment chamber supplied with fresh air by a vertical tube open 1353 4 5 at its lower end. Outstandingly high air-to-gas ratios are [58] Fieid 126/39 achieved by self-producing noise to disturb a jet stream 239/43; of natural gas emanating from a nozzle. One important construction is the use of an approximately rectangular References Cited electric discharge machined nozzle orifice having a Crannell et al 126/39 E length-to-width ratio greater than about 3:].

2 Claims, 3 Drawing Figures BACKGROUND-OF THE INVENTION This invention relates to fluid fuel burning apparatus and, more particularly, to a system for supplying uncontaminated'air for combustion to a primary aerated pilot burner for igniting the upper burner in a two burner oven. I When the lower (bake) burner is in operation, the air surrounding theupper (broil) .pilot becomes contaminated and oxygen depleted, causing the pilot to be snuffed out.

In the past, it has been the practice to supply the upper pilot with fresh air by means of an air supply tube, terminated at its inlet end in an uncontaminated air zone within the oven or burner compartments and at its outlet end in the primary air intake of the pilot. Note that primary air is that air which is eventually mixed with the gas jetting from the pilot burner through the burner orifices.

With sufficient uncontaminated primary air supplied through the tube, the pilot will burn stabely even when surrounded by a contaminated atmosphere. The primary air is drawn through the tube by the relatively weeak air-entraining effect of the orifice and pilot. However, the tube itself has a certain flow resistance. Further, the air within the tube is often colder, hence heavier, than the air within the overn, causing further resistance to flow. xhese factors, taken with the limited air entrainment capability of conventional orifices at commonly low gas pressures make an air-to-gas ratio of 8:1 (usually the minimum required) impossible. This is true because the low gas pressures cannot establish a. sufficiently strong gas jet from an orifice to pull the heavy, cold, fresh air upwardly against the flow resistance of the tube.

SUMMARY OF THE INVENTION the prior art are overcome by providing an aspirator including a jetnozzle with an electric discharge ma chined (EDM) orifice.

In accordance with the present invention, it has been 7 found than an elongated or slot-shaped EDM orifice having a length-to-width ratio in excess of about 3:] works very reliably (will produce an air-to-gas ratio of 8:1 or more) and may be manufactured at a reasonable cost with substantially a 100 percent yield (no rejects). On the other hand, a circular or square orifice will not work at all. Further, if the orifice is not an EDM 'slot, yield drops to about fifty percent, which is wholly impractical.

It is known that sound vibrations will increase the air entrainment capacity of an orifice and receiver, particularly at lower gas pressures. For use herein, the phrase "critical value is used to mean that sound frequency and intensity which will make it possible to achieve an air-to-gas ratio to the pilot in excess of about 8:1. The construction of the invention-described hereinbefore will create such sound vibrations.

The above-described and other advantages of the invention will be better understood from the following description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative;

FIG. 1 is a schematic diagram of a two burner oven;

FIG. 2 is a vertical sectional view through pilot light apparatus of the invention; and

FIG. 3 is an end elevational view of a nozzle shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIEMNT The upper main burner is indicated at 10 in FIG. 1. The lower main burner'is indicated at 11. When the burner 11 is turned on, the upper pilot is cheated out of oxygen or fresh air. If some device is not employed to remedy this situation, the upper pilot will go out. The upper pilot burner is indicated at 12. A fresh air or snorkel tube 13 provides fresh air to burner 12. Tube 13 goes out through the oven wall at 14 and back into the oven at 15. The oven wall is indicated at 16. The lower end of the tube 13 is indicated at 17. Tube end 17, by being located below lower burner 11, receives fresh air. The bottom wall 18 of the oven has holes. Fresh air comes into the oven through these holes. It is necessary to bring tube end 17 back to a position inside the oven because the upper pilot light will otherwise be put out when the oven doors slams.

There has been considerable difficulty in finding a mechanism which will draw sufficient air upwardly through tube 13. This is due to the fact that the cold air at the bottom of the oven is heavier than at the top of the oven. It is also due to the fact that there is a flow resistance in tube 13.

The system of the present invention is indicated in FIG. 2. Gas is supplied through an orifice 19 in a nozzle 20. Air is drawn up through tube 13. A gas-air mixture is then jetted into a receiving tube 21. Pilot burner 12 is fixed to the end of receiving tube 21.

Some of the problems regarding snorkel pilot systems are outlined in us. Pat. Nos. 3,320,943 and 3,338,321.

The chief problem is that the pressure of the gas inside nozzle 21 is so low that sufficient air canoot be raised in tube 13 and supplied 'to the pilot burner through tube 21 with the gas emanating from orifice 19. The ratio of air-to-gas supplied to the pilot burner through tube 21 should be about 8:1, 9:1, or more. In many places, the gas pressure is equal to four inches of water. There would be little or no problem if the gas pressure were ten or twelve inches of water and higher.

One of the outstanding discoveries which was made was that orifice 19 should be rectangular as indicated in FIG. 3. A rectangular orifice 13 mils long and four mils wide is preferred. A round or square oficie will not work. The length-to-width ratio must be in excess of about 3:1.

Another outsanding advantage of the present invention is that when the rectangular orifice 19 is made, it is made by electric discharge machining. This improves the operation of the orifice to an extraordinary degree.

According to the invention, the orientation of slot 19 is immaterial. That is, it may vertical, horizontal, or at any angle. Nozzle 20 is 3 mils thick. It preferably is Orifice 19 produces a jet stream or flow of gas as indicated at 22. The flow is hereby defined as a vortex flow pattern.

The amount of air which is picked up or entrained by gas flow 22 is hereeby defined as the air entrainment capaicty of the jet stream 22. What is claimed is:

l. A system forproviding a mixture of air and a gas fuel, said system comprising: means defining an air entrainment chamber; a receiver tube connected from said chamber in a manner to receive air and a gas fuel therefrom; a pilot burner connected from said receiver tube in a manner to receive air and a gas fuel therefrom, said burner having a head with a flame port; a gas fuel nozzle fixed inside said chamber in a position in I alignment with said tube, said alignment being such that when a gas jet is produced in said chamber by a flow of gas fuel through said nozzle, said jet flows in a direction toward the interior of said receiver tube, said nozzle being adapted to inject a stream of gas fuel through said chamber and through said receiver tube to said burner head; and an air supply tube having one end connected to said chamber, said air supply tube extending downwardly from said chamber to its other end, said other end being open, said air supply tube being hollow and providing free and open communication from the interior of said chamber to said open end thereof, said nozzle having an orifice to allow the escape of a gas fuel therefrom, said orifice being approximately rectangular and having a length-to-width ratio in excess of about 3:1.

2. The invention as defined in claim 1, wherein said orifice is electric discharge machined. 

1. A system for providing a mixture of air and a gas fuel, said system compRising: means defining an air entrainment chamber; a receiver tube connected from said chamber in a manner to receive air and a gas fuel therefrom; a pilot burner connected from said receiver tube in a manner to receive air and a gas fuel therefrom, said burner having a head with a flame port; a gas fuel nozzle fixed inside said chamber in a position in alignment with said tube, said alignment being such that when a gas jet is produced in said chamber by a flow of gas fuel through said nozzle, said jet flows in a direction toward the interior of said receiver tube, said nozzle being adapted to inject a stream of gas fuel through said chamber and through said receiver tube to said burner head; and an air supply tube having one end connected to said chamber, said air supply tube extending downwardly from said chamber to its other end, said other end being open, said air supply tube being hollow and providing free and open communication from the interior of said chamber to said open end thereof, said nozzle having an orifice to allow the escape of a gas fuel therefrom, said orifice being approximately rectangular and having a length-to-width ratio in excess of about 3:1.
 2. The invention as defined in claim 1, wherein said orifice is electric discharge machined. 